BECKER, M. L.¹, E. T. RASBURY², G. N. HANSON¹, G. C. NADON³, and E. H. GIERLOWSKI-KORDESCH^3
1SUNY Stony Brook, Stony Brook, NY
²Queens College, Flushing, NY
³Ohio University, Athens, OH

Abstract: U-Pb Age of a Palustrine Limestone, Monongahela Group, Southeast Ohio: Potential for Dating Terrestrial Sections

The upper Paleozoic strata of southeastern Ohio is cyclic and mostly non-marine with sparse biostratigraphic control. We are investigating the potential of using the abundant lacustrine and palustrine limestones for U-Pb dating to establish the time of sedimentation of this non-marine section. Seven aliquots of organic rich calcite from a palustrine limestone of the Virgilian Monongahela (directly below the assumed PennsylvanianPermian boundary) have uniform Pb concentrations of about 2 ppm; U concentrations range from 16 to 30 ppm. Values of ²⁰⁶Pb/²⁰⁴Pb range from 44 to 83. The sample yields a concordant age of 268 +/- 26 Ma (MSWD = 8.6) on a 3-D concordia plot. Considering its relatively large uncertainty this age is only slightly younger than the Pennsylvanian-Permian boundary (302 + 2.4 Ma, Rasbury et al.). The initial Pb isotopic composition (²⁰⁶Pb/²⁰⁴ Pb = 1 7.6 +/- 2.5) is reasonable for the time of sedimentation suggesting the system has not been disturbed. The relatively large range in the U-Pb ratios for these low Mg calcite rocks gives us reason to expect that we should be able to develop approaches using palustrine limestone for dating the time of sedimentation in this area more precisely.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas